1. Field of the Invention
This invention relates generally to circuitry for developing a true, symmetric or bipolar, absolute value output signal from an input signal arising from, for example, a charge stored in a charge coupled device (CCD) structure. Such circuitry is also referred to hereinafter as a "general absolute value circuit". More particularly, the invention relates to a general absolute value circuit that is compact enough to be used on a sensor chip as part of, or in combination with, a pixel processor. Such processors find application in imaging systems and other systems that collect electromagnetic radiation (EMR), such as light, as part of circuitry included on a sensor chip and designed to improve performance and speed of systems in which they are incorporated.
One aspect of the invention relates specifically to a general absolute value circuit comprised of a balanced differential amplifier combined with a dual shelf transistor structure. The balanced differential amplifier, in response to an input signal, drives the dual shelf transistor structure which in turn generates the desired true absolute value output signal. Such circuitry may, for example, be used in imaging systems to implement focal-plane processing algorithms, and may be more generally used for performing a single read (with respect to stored charge) true absolute value computation by a pixel processor situated on a sensor chip.
Another aspect of the invention relates to an improved shelf transistor structure which may be used to further enhance performance and speed of any system in which the general absolute value circuit of the invention is incorporated.